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article imageAurornis, Archaeopteryx-like ancestor of birds found in China

By JohnThomas Didymus     May 30, 2013 in Science
Paleontologists say they have found the fossilized remains of a new avialan, or basal bird, which re-establishes the position of Archaeopteryx as part of the group of basal birds ancestral to modern birds.
The complete fossil remains of the chicken-sized Aurornis xui (Aurornis: "dawn bird") found preserved in a shale slab, was estimated to be about 160 million years old, and about 10 million years older than the famous Archaeopteryx.
The basal bird, about 20 inches in length, with small triangular teeth and primitive-type feathers, was discovered in the famous fossil beds of a quarry in the Liaoning Province of northeastern China, near the North Korean border.
In the study titled: "Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds," published in the journal Nature, lead author Pascal Godefroits of the Royal Belgian Institute of Natural Sciences and his colleagues, carried out a broad taxonomic study of the types of fossil bird-like animals that have been discovered from the Jurassic and Cretaceous era.
Working with their Chinese counterparts, the Belgian researchers conducted a re-assessment of the classification of the different species. They classified both Aurornis and Archaeopteryx in the family Avialae, a group of bird-like dinosaurs believed to be an evolutionary link between reptiles and modern birds.
LA Times reports that Luis Chiappe, a vertebrate paleontologist at the Natural History Museum of Los Angeles, who was not involved in the study, said: "It pushes [back] the origins of birds — or origin of animals that are very closely related to the bird. And that’s quite exciting."
He added: "Around the origin of birds 160 million or so years ago, there were many fossils that were experimenting with birdness — getting more and more bird-like. What exactly the line is that made it to birds is not entirely clear … and this is just one candidate."
He continued: "You’re looking at an animal that is either a very primitive bird or something very closely related to birds. I tend to think that it’s not a bird, but that it’s one of those true very close ancestors of bird."
Aurornis xui
Aurornis xui
Godefroit et al.
Avialans are a group of dinosaur-birds the diverged millions of years ago from theropod dinosaurs, a group that includes Tyrannosaurus Rex. When Archaeopteryx was first discovered in Jurassic limestone in Germany in 1861, it was hailed as the "first true bird," but subsequent discovery of specimens of fossil theropods with feathers led some experts to question the status of Archaeopteryx as being in a line directly ancestral to modern birds. This led to the reclassification of Archaeopteryx as a theropod dinosaur. The reclassification caused some confusion because the broad consensus that Archaeopteryx could fly, or at least glide, suggested that the power of flight could have evolved in two separate evolutionary lines.
The reinstatement of Archaeopteryx in the family Avialae, considered transitional between reptiles and birds, simplifies the picture once again by establishing "a single [line] of origin of powered flight."
The study also reclassified another group of bird-like bipedal threopods, the Trodontidae, as related to the avialans.
Godefroits told the BBC: "This new comprehensive phylogeny, or evolutionary development, shows that at point of origin avialans were already diversified in northern China during the Middle-Late Jurassic. Previous phylogenetic investigations were based on maybe only 200 morphological characteristics. Here, we recognise almost 1,500 characteristics. So it's a much bigger and more robust analysis, and according to this new investigation Archaeopteryx is again considered an ancestor of birds and the new creature we describe is also a basal bird; and in fact it is even more primitive than Archaeopteryx."
With regard to Trodontidae, the BBC reports that Dr Paul Barrett of the Natural History Museum in London, said: "What we're arguing over here is actually very small, esoteric features of the anatomy. We're looking at a nexus of animals around bird origins - birds themselves and a bunch of dinosaurs that are almost, but not quite, birds. There is a really grey, wobbly line between the two. Just one or two changes across a huge body of data can make the difference between an animal being on one side of this bird-dinosaur divide or the other."
Barret concluded: "The beginnings of the bird line is all about fine-tuning parts of their anatomy - of their wings, of their hips, of their chest muscles and shoulder girdles, and so on - to make them flight-ready."
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